Electrical devices typified by batteries and electrolytic capacitors are manufactured by filling a case which is made of metal or the like and which contains an electrode group with an electrolytic solution and then sealing the case, where the electrode group is an electrical device element.
Conventionally, a case placed upright is filled with a predetermined amount of electrolytic solution and left at rest for an extended period of time to allow the electrolytic solution to gradually permeate spaces in the electrode group. However, since an electrode group is generally made of electrode plates stacked densely, it takes time to allow the electrolytic solution to permeate the spaces in the electrode group. The case needs to be left at rest, for example, for a whole day and night in order for the electrolytic solution to permeate the spaces among the electrodes on its own. This means very inefficient production.
Also, since the electrolytic solution is absorbed very slowly, if the required amount of electrolytic solution is supplied at once into the case, the electrolytic solution will overflow the case. Methods adopted to deal with this situation include a method in which a watertight cover is placed on an opening of the case and filled with a predetermined amount of electrolytic solution. However, the method involves placing the covers one by one on the cases, making it difficult to increase manufacturing efficiency.
Japanese Patent No. 3467135 discloses an electrolytic-solution filling method intended to solve this problem. The method depressurizes an opening of a case, fills the opening with the electrolytic solution to temporarily form a pool, fills the depressurized case with the electrolytic solution, allows the electrolytic solution to permeate spaces in an electrode group, and then increases pressure in the case to make the electrolytic solution in the pool permeate the spaces in the electrode group.
By depressurizing the case once, the method expels air from the spaces in the electrode group so that the air will not obstruct permeation of the electrolytic solution. After creating a condition in which the electrode can permeate the spaces easily, the method fills the case with the electrolytic solution. Then, the method further pressurizes the case to cause the electrolytic solution in the pool to permeate. The combination of depressurization and pressurization not only reduces the time required for the electrolytic solution to be absorbed, but also prevents the electrolytic solution from spattering upon pressure release.